Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
They contribute in several ways. Firstly, they keep the fans engaged between movie releases. They also introduce new concepts and ideas that might later be incorporated into the movies. For instance, some new villains or plot twists can first be tested in the graphic novels. Also, they can provide different interpretations of the characters, adding more dimensions to the overall MCU franchise. Moreover, they can attract new fans who are more into reading graphic novels rather than just watching movies.
Not always. While the MCU draws inspiration from the comics, there are often changes and adaptations made to fit the cinematic universe and modern audiences.